Magnetic proximity switches



Jan. 30, 1962 w. B. MINToN 3,019,321

MAGNETIC PROXIMITY SWITCHES Filed April 8, 1959 2 Sheets-Sheet 1 I N V EN TOR. M995 B. /Y//vm/v A frog/Veys Jan. l.310, 1962 w. a; MlNToN :MAGNETIC PRoxmm' SWITCHES Filed April 8, 1959 INVENTOR.

United States Patent O The present invention relates generally to magneticallyactuated electrical switches and moreparticularly to a proximity device incorporating ka mercury contact switch n which is actuated by a magnetic sensing element.

Magnetically-operated proximity switches are known which respond to changes in distribution of flux resulting from the presence of an automobileor other ferromagnetic mass. Such switches may be used as sensing elements to control the reset mechanism of parking meter in the manner disclosed, for example, in the copending application of Minton etal., Serial No. 686,329, led September 26, 1957, for Automatic Cancelling or Re- Setting Parking Meter Unit.k They are also useful for controlling *ther operating mechanism of doors and to carry out other proximity functions.y

When the magnetic proximity switch acts as a detector f or vehicles, it'normally occupies an exposed position on the post of the parking meter land is subject to shocks and other mechanical disturbances. Conventional switches for this purpose suffer `from a number of serious drawbacks, ,among which are low sensitivity, instability of operation and lack of mechanical balance. As a consequence, the switch may fail to respond if the vehicle is somewhat distant from the meter and yet within the prescribed parking area. On the other hand, a false response may occur in the event the post is struck or by reason of disturbances in the vicinity of the meter. The unreliability and erratic operation of conventional magnetic switches has militated against their widespread use in parking meters and in other exposed situations.

In View ofthe foregoing, it is the primary object of this invention to provide a magnetically-actuated proximity switch of efficient and balanced design, the switch being highly sensitive to the presence of ferromagnetic objects in the switch vicinity. An important advantage of the invention is that the switch is capable of heavy dutyk `high-current switching action, thereby obviating the need for auxiliary relays.

More specically it is an object of the invention to provide a compact and rugged switchof the above-noted type which is mechanically stable, hermetically sealed and adapted for constant use under varying and diiiicult ambient conditions.

A significant feature of the invention resides in a buoyant rotor which houses the switch and riloats in a damping iluid whereby lthe switch is highly sensitive to changes in magnetic flux but is dampened against mechanical disturbances, thereby avoiding spurious actions. Also an object of the invention is to provide a magnetically-actuated switch incorporating externallycontrolled compensators for accurately kzero-setting the switchvIt is yet another object of the invention to provide a magnetic proximity switch which is so shielded as to respond positively only to changes of ux within a prescribed area.

Brielystated, these objects are attained in a switch structure constituted by a mercury-switch capsule nestled withina ring magnet polarized in a direction normal to its central axis, the capsule and ring assembly being mounted within" a buoyant rotor which is floatably supported by la uid medium within a sealed casing, whereby said rotor is caused to turn in response to the presence of a ferromagnetic mass to effect a switching action. :For ka better understanding of the invention as well as other objects and further features thereof, reference is 3,019,321 Patented Jan. 30, 1362 'ice ` conjunction with the vattached drawing wherein like cornponents in the several views are identified like refer- Lence numerals.

v ln the drawings:

FIG. l is a perspective view of a preferred embodiment of a magnetic proximity switch in accordance with the invention.

FIG. 2 is a section taken through the indicated by line 2--2 in FIG. l. Y

FIG. 3 is a transverse section taken kin the plane indicated by line `3--3 in FIG. 2.

ElG. 4 is an end elevational view of the proximity switch.

FIG. 5- shows, in perspective, the compensating elements of the switch. i'

FIG. 6 is a first alternative form of mercury switch, shown in section.

y FG, 7 is a second alternative form of mercury switch, shown in section. d

FIG. 8 is a transverse section taken through the plane indicated by lines 3-,8 in FIG. 7.

' Referring now to Ithe drawings, and more particularly to FGS. l to 5, the principal components of the proximity device are a mercury switch capsule, generally designated by numeral 1t), a kring magnet 11, and a buoyant rotor 12 for housing the ring magnet and capsule assembly, the rotor iioating within a cylindrical casing 13 of insulating material.

The mercury switch capsule 10 is constituted by a cylindrical kcup 14 hermetically enclosed by a cap 1,5 to define a circular inner cavityl 16 containing a small pool of mercury 17. The cup and cap 14 and 15 are formed of insulating material. 'Inserted within vthe cup and cap respectively at corresponding positions adjacent the periphery of the capsule vare conductive plugs 18y and 19, the inner ends of the plugs being ush with the walls of the cavity 16. The outer ends of plugs 13 yand 19 engage metallic flat springs 2i) and 2,1 to which are centrally attached conductive shafts 22 and 23, respectively, which extend on either side of the capsule VKalong the horizontal axis X of rotation thereof.

The mercury switch capsule 10 is positioned in the vertical plane ywhereby the mercury pool 17 always remainson the bottom of cavity 16 regardless of the angular position of the capsule. Consequently, an electrical connection is made between plugs `18` and 19 only when the plugs are positioned -to engage the mercury pool. This occurs only for one angular position of the capsule, and when as demonstrated in FIG. 3, the capsule is rotated about its axis, contact between plugs is broken.

Capsule 10 is nestled snugly within ring magnet 11, the magnet having a rectangular cross-section and being formed preferably of ferro-ceramic material, such as ferroxcube or other magnetic material polarized in a direction normaly to the central axis of the ring. Thus the presence of ay ferromagnetic body in the proximity of the ring causes a change in ilux distribution tending to cause rotation of the ring and of the capsule received therein.

Ring 11 is mounted centrally within the tubular insulating shell 24 of the drum-shaped rotor 12, the ends of the shell being sealed airtight by insulating discs 25 and 26. The magnetic ring and capsule assembly are rmly held Within the rotor by insulating spiders Z7 and 28 engaging the opposing sides of the assembly and supported kby sleeves 29 and 30 which surround the conductive shafts `22 and 23 and are integrally attached to the end discs 2K5 and 26 of the rotor. The rotor 12 is otherwise hollow and is buoyant, the rotor floating in a longitudinal axis dielectric fluid F such as silicone oil whichwlls the annular space between the-rotor and the cylindrical casing 13.

The ends of casing 13 are enclosed by rectangular insulating blocks 31 and 32. Interposed between the blocks 31 and 32 at either end of the rotor 12 and immersed in the fluid F are conductive spring bearings 33 and 34 in which are journalled the ends of the shafts 22 and 23, whereby the rotor l2 is coaxially disposed within the casing 13 and is rotatable therein. Electrical connections to the capsules are made through terminal posts 35 and 36 mounted on the casing 13 and connected to the spring bearings 33 and 34. The terminals may be provided with washers to prevent leakage of the fluid. Thus terminal 35 is connected to plug 19 through bearing 33, shaft 23 and spring 21, while terminal 36 is connected to plug 18 through bearing 34, shaft 22 and spring 20.

It will be seen that the capsule and ring assembly and the rotor and casing combination are symmetrically arranged and fully balanced. The rotor turns freely on its axis, the only friction encountered being at the shaft bearings. The fluid within the casing acts to dampen rotation of the rotor to prevent transient and erratic operations.

The casing is surrounded by a rectangular magnetic shield 37 which encompasses the whole unit and is open only at the front of the casing, thereby confining the action of the proximity switch to objects within the field projecting from the opening. The switch is therefore insensitive to objects outside of the field and will not be influenced by the presence of objects behind or to the sides thereof. It will be obvious that by properly shaping the shield any desired field configuration may be obtained.

In order to set the static position of the rotor, two pairs of intermeshed gears 38 and 39, and 40 and 41 are provided in a circular recess 42 formed in the end block 32. As best seen in FIG. 5, the gear pairs lie in parallel planes with paired centers 180 apart. Embedded within each gear is a bar magnet 43. An outside knob 44 is coupled to gear 38 whereby the magnets on gears 38 and 39 may be simultaneously rotated from parallel to co-linear positions. An outside knob 45 is coupled to gear 41 whereby a similar action may be effected with the magnets on gears 40 and 41.

Thus the compensator for the switch is constituted by four magnets each effectively in a quadrant and angularly adjustable to produce a constant magnetic field which acts on the field of the ring magnet whereby the initial setting of the ring may be caused to assume any desired position. The initial ring position may be such as to provide an open switch or a closed switch, and when the switch is actuated by the presence of a body, the switch is caused to close or open depending on the initial status of the switch.

When the ferromagnetic body to be detected is nonpolarized, such as an automobile, the mercury switch will always rotate in a given direction. However, should the body be polarized, then the direction of rotation will depend on the relative polarizations of the body and the ring magnet. In order to effect a switching action regardless of the direction of ring movement, a modified capsule is provided as shown in FIG. 6 in which a pair of plugs 18 and 18" is provided on one side of the cavity, the plugs being angularly displaced in opposing position relative to the vertical so that plug 18 is engaged by the mercury when the switch turns in one direction and plug 18" is engaged when the capsule turns in the opposing direction.

An alternative form is shown in FIGS. 7 and 8 where the capsule is constituted by a double cup 46 of insulating material, each cup being enclosed by a conductive plate 47 and 48. A pair of holes 49 and S0 is bored through the base wall of the cup on either side of the vertical such that mercury 51 is permitted to fiow through one hole to effect a connection between the plates when the capsule is turned in one direction, and ows through the other hole when the capsule is turned in the reverse direction.

While there has been shown what are considered to be preferred embodiments of the invention, it will be manifest that many changes and modifications may be made therein without departing from the essential spirit of the invention. For example, the mercury switch capsule may be of any standard type, such as that disclosed in the Payne Patent 2,101,092 or any other commercially available mercury switch which is position sensitive and is adapted to t within the ring magnet. It is intended, therefore, in the annexed claims to cover all such changes and modifications as fall Within the true scope ofthe invention.

What is claimed is:

l. A proximity switch comprising a mercury switch capsule, means supporting said capsule for rotation about a predetermined axis whereby a switching action occurs at a predetermined angular position of the capsule, and a ring magnet surrounding said capsule and polarized in a direction normal to said axis whereby said capsule is caused to rotate when a ferromagnetic body is proximate thereto.

2. A switch, as set forth in claim 1, further including an adjustable magnetic compensator disposed adjacent said magnet to establish a magnetic field so interacting with the field of the ring magnet causing said capsule to assume a desired static position.

3. A magnet and switch assembly comprising a ring magnet polarized in a direction normal to the central axis thereof and a mercury switch capsule attached to said magnet and fixed axially relative thereto and including a mercury pool in a cavity which is engageable by contact elements when the assembly assumes a predetermined angular polar position relative to said axis.

4. A proximity switch as set forth in claim 1, wherein said mercury capsule comprises a cylindrical container of insulating material having a circular cavity therein, a mercury pool in said cavity, and a pair of conductive plugs inserted in opposing end walls of said container at corresponding positions therein whereby a connection therebetween is effected by said mercury when said capsule is caused to assume a given polar position relative to the longitudinal axis of the container.

5. A proximity switch as set forth in claim l, wherein said mercury capsule comprises a cylindrical container of insulating material having a circular cavity therein and two pairs of conductive plugs, each pair of plugs being inserted in opposing end walls of said container at corresponding positions therein, the pairs being angularly displaced relative to each other whereby a connection between plugs in a pair is effected when the capsule is caused to assume a given polar position relative to the longitudinal axis o-f the container.

6. A proximity switch as set forth in claim 1, wherein said mercury capsule comprises a cylindrical casing having conductive end plates and an insulating central partition dividing said casing into two circular cavities, said partition having at least one bore therein communicating between said cavities, and mercury pools in said cavities providing a connection between said end plates when said capsule is oriented to permit mercury to fiow through said bore.

7. A proximity switch comprising an assembly constituted by a ring magnet polarized in a direction normal to its central axis and a mercury contact switch capsule attached to said ring magnet and adapted to produce a switching action at a predetermined polar position of said assembly relative to said central axis, a buoyant rotor enclosing said assembly and rotatable about an axis coincident with said central axis, and a pair of shafts supporting said rotor at either end thereof and connected to the contacts of said switch therein.

8. A proximity switch comprising an assembly constituted by a ring magnet polarized in a direction normal within said ring magnet and adapted to produce a'switching action at a predetermined polar position relative to said central axis, a buoyant rotor housing said assembly and rotatable about an axis coincident with saidr central axis, a sealed casing surrounding said rotor and spaced therefrom, and a tiuid medium lling the space between said rotor and said casing to dampen rotation of the rotor.

9. A proximity switch comprising a tubular casing, a drum-shaped hollow rotor concentrically disposed within said casing and mounted therein for rotation about a central longitudinal axis, a ring magnet received centrally within said rotor and polarized in a direction normal to said axis of rotation, a mercury switch capsule nestled within said magnet and adapted to produce a switching action at a given polar position of said rotor, and a uid medium lling the space between said rotor and said casing to dampen rotor movement. f

10. A proximity switch comprising a tubular casing enclosed at either end by insulating blocks, a drum-shaped hollow rotor concentrically disposed within said casing and mounted therein on a pair of shafts for rotation about a central longitudinal axis, -a ring magnet received cenrtrally within said rotor and polarized in a direction normal to said axis of rotation, a mercury switch capsule nestled within said magnet and adapted to produce a switching action at a given polar position of said rotor, said capsule having contact terminals connected to said shafts, and a uid medium lling `the space between said f rotor and said casing.

1l. A proximity switch, as set forth in claim 10, further including a magnetic compensator mounted in a recess in one of said 4blocks and constituted by two pairs of intermeshing gears disposed in separate parallel planes at quadrature positions, each gear having a bar magnet embedded therein.

References Cited in the file of this patent UNITED STATES PATENTS 1,844,413 Walker Feb. 9, 1932 2,459,968 Schwartz r.. Ian. 25, 1949 2,498,212 Laverall et al Feb. 2l, 1950 2,550,073 Lindstrom Apr. 24, 1951 2,597,080 Glickman May 20, 1952 2,709,738 Walter May 31, 1955 

